The present invention relates generally to fluid treatment Systems and, in particular, to a storage tank and storage tank control valve for use with a fluid treatment system, such as a reverse osmosis system.
It is known to use a storage tank to store a processed fluid produced by a fluid treatment system. For example, reverse osmosis systems are used to produce potable or drinking water from water sources that contain undesirable contaminants, etc. In a typical reverse osmosis system, especially in the type of reverse osmosis system used in homes, the rate at which treated water or xe2x80x9cpermeatexe2x80x9d is produced by the system can be very low. As a result, a storage tank is used to store permeate, so that relatively large quantities can be made available when the consumer opens the tap or faucet. In the past, xe2x80x9cprechargedxe2x80x9d storage tanks are used. In this type of storage tank, a bladder is used to define a pressurized chamber, usually filled with a compressible gas, such as nitrogen. The bladder isolates the gas from the processed water received by the tank. As processed water or xe2x80x9cpermeatexe2x80x9d (in the case of a reverse osmosis system) is received by the tank, it gradually compresses the gas in the pressurized chamber. As a result, the permeate is stored under pressure, such that when the faucet is opened, the pressure in the storage tank exerted by the compressed gas, forces permeate out of the tank and to the faucet.
Although these storage tanks are widely used and provide a suitable means for storing permeate, they do have a significant drawback. As more and more permeate is received by the tank, the pressure needed to effect flow of permeate into the tank increases because as the gas chamber is compressed, forces on the bladder increase. Accordingly, in order to completely fill the storage tank, a significant pressure must be applied to the permeate as the capacity of the tank is reached. This resistance to flow exerted by the tank in itself decreases production rate of the reverse osmosis system, since the reverse osmosis system relies on differential pressures between the source and the output to effect flow across the membrane. In addition, as permeate is discharged by the tank, its delivery pressure is gradually reduced as the pressurized gas chamber expands. As a result, the delivery pressure varies significantly between a full tank and a nearly empty tank.
The present invention provides a new and improved fluid treatment system that includes a storage system for storing processed fluid such as water. The storage system receives the processed fluid at substantially zero pressure and discharges the stored fluid at a pressure that is substantially the pressure of the source of fluid being treated.
In the preferred and illustrated embodiment, the invention is disclosed in connection with a reverse osmosis unit. It should be understood, however, that the invention has broader applicability and should not be limited to a reverse osmosis application.
In accordance with the invention, a storage system is disclosed for storing treated or processed water discharged by a water treatment unit. The storage system includes a tank assembly having an outer tank housing that encloses an expandable bladder. A pressurizing region is defined between an outside of the bladder and an inside of the outer tank housing. A control valve is disclosed that controls the communication of source water under pressure with the pressurizing region and also controls the communication of the pressurizing region with a drain, so that under predetermined operating conditions, source water in the pressurizing region is allowed to flow to a drain in order to allow the bladder to expand as it receives treated water.
In the illustrated embodiment, the control valve includes a fluid pressure operated control device that is responsive to a dispensing device through which the treated water is dispensed. In particular, the control device is operative to connect the source water to the pressurizing region when the dispensing device is dispensing treated water and is operative to communicate the pressurizing region with the drain when the dispensing device is not dispensing water.
In the preferred embodiment, the control device includes a pilot valve responsive to fluid pressure in a supply conduit feeding the dispensing device and is movable between at least two positions. A servo valve also forms part of the control device and is responsive to the positions of the pilot valve.
The pilot valve includes a source water port, a common port and a drain port and further includes a piston operated flow control member for controlling the communication between the common port and the source port and between the common port and the drain port. Similarly, the servo valve includes a source water port, a common port and a drain port, as well as a piston operated flow control member for controlling the communication of the common port with either the source water port or the drain port. The ports of the servo valve are sized to permit relatively unrestricted flow and, hence, the servo valve controls the flow of source water to the pressurizing region of the tank assembly, and the flow of source water from the pressurizing region to the drain.
In a more preferred embodiment, the water treatment unit disclosed is a reverse osmosis nodule having a permeate output, a source water input and a concentrate output. In the illustrated reverse osmosis system a prefilter is positioned upstream of the reverse osmosis module and fitter source water before it enters the reverse osmosis unit and the pressurizing region of the tank. According to a further feature of this embodiment, a post filter filters permeate before it is delivered to the dispensing device, e.g., a faucet or tap.
According to a preferred embodiment, the control valve assembly for controlling the pressurization and depressurization of the pressurizing region of the tank is mounted directly to the tank. In accordance with this embodiment, the tank includes an internally threaded neck which is adapted to receive external threads formed on the control valve or housing. The control valve assembly is threaded into the neck of the tank and is easily removed for service or replacement.
According to another feature of the invention, a lower portion of the control valve assembly includes a depending, threaded segment which, in conjunction with a internally threaded retaining nut serves as a securement for the elastomeric bladder contained within the tank. According to this preferred embodiment, the retaining nut includes a radial flange which supports a bladder retaining bearing. As the retaining nut is threaded onto the lower segment of the valve, the bearing captures a neck of the bladder between itself and a tapered segment on the control valve, thus securing the bladder to the control valve. The bearing ring facilitates rotation of the retaining nut when either installing or removing the bladder.
Additional features of the invention will become apparent and a fuller understanding obtained by reading the following detailed description made in conjunction with the accompanying drawings.